Heretofore, in a device that controls an electric actuator for use in a variable valve device or the like of an internal combustion engine (engine), for example, there has been known a technique as in Patent Document 1, in which a sensor that measures a position of a valve timing control system (VTC) is provided, and the position is controlled to a target position based on a measurement result of the sensor. In Patent Document 1, a motor rotation speed sensor is provided in a motor for varying a turning speed of a planetary gear in a phase variable mechanism, and a position of the VTC is detected by a rotation signal of a motor shaft, in which a detection frequency is higher than that of a rotation signal of a camshaft.
As described above, the motor rotation speed sensor is provided, whereby such a VTC position can be detected even during a period while the rotation signal of the camshaft cannot be detected, and a valve timing control with good accuracy in a low revolution range of the engine is realized. A VTC position detection system composed by addition of the sensor as described above does not depend on the number of revolutions of the engine, and accordingly, can ensure controllability even at the time when the number of revolutions of the engine is low.